Jeff The Killers Swing Animation Server-Sided

local Players = game:GetService("Players")
local UserInputService = game:GetService("UserInputService")
local player = Players.LocalPlayer

local hitId       = "rbxassetid://54584713" -- the swing animation, is replacable and supports r15 or r6
local hitSpeed    = 1.0 -- speed of the animation i suppose
local hitFadeTime = 0.1 -- how smooth can the animation end
local hitPriority = Enum.AnimationPriority.Action -- layers of animation, now above idle and walk (and run, and jump, and fall)

local hitAnim = Instance.new("Animation")
hitAnim.AnimationId = hitId

local currentHitTrack = nil

local function playHit()
    local char = player.Character
    if not char or not currentHitTrack then
        return
    end

    if currentHitTrack.IsPlaying then
        currentHitTrack.TimePosition = 0
    else
        currentHitTrack:Play(hitFadeTime, 1, hitSpeed)
    end
end

UserInputService.InputBegan:Connect(function(input, gameProcessed)
    if gameProcessed then return end
    if input.KeyCode == Enum.KeyCode.Z then
        playHit()
    end
end)

local function setupCharacter(character)
    if currentHitTrack then
        if currentHitTrack.IsPlaying then
            currentHitTrack:Stop(0)
        end
        currentHitTrack:Destroy()
        currentHitTrack = nil
    end

    local humanoid = character:WaitForChild("Humanoid", 5)
    if not humanoid then
        return
    end

    local animator = humanoid:FindFirstChildOfClass("Animator")
    if not animator then
        animator = Instance.new("Animator", humanoid)
    end

    currentHitTrack = animator:LoadAnimation(hitAnim)
    currentHitTrack.Looped = false
    currentHitTrack.Priority = hitPriority
end

player.CharacterAdded:Connect(setupCharacter)

if player.Character then
    task.spawn(setupCharacter, player.Character)
end